1. Field of the Invention
The present invention relates to a magnetic information recording/reproducing field, particularly to a magnetic head and a magnetic recording/reproducing apparatus for recording/reproducing information on a magnetic recording medium by using the magnetic head, and more particularly to a magnetic head using a magnetoresistance effect based on ferromagnetic tunnel junction, a method of manufacturing the magnetic head, and a magnetic recording/reproducing apparatus using the magnetic head.
2. Description of the Related Art
In connection with recent compact and large-capacity design of magnetic recording/reproducing apparatuses, a magnetoresistance effect type head capable of realizing a large reproduction output (hereinafter referred to as xe2x80x9cMR headxe2x80x9d) has been practically used. The MR head has been disclosed in a paper titled xe2x80x9cA Magnetoresistivity Readout Transducerxe2x80x9d of xe2x80x9cIEEE Trans. on Magn., MAG7 (1971) 150xe2x80x9d, for example. NiFe film is generally used as the magnetoresistance effect material, and in the case of a magnetoresistance effect type element (hereinafter referred to as xe2x80x9cMR elementxe2x80x9d) using the NiFe film, the magnetoresistance variation rate corresponding to the reproduction output of the head is equal to about 2 to 3%.
FIG. 14 is a cross-sectional view showing a composite magnetic head (hereinafter referred to as xe2x80x9ccomposite headxe2x80x9d) equipped with a reproducing head based on an MR element and a recording head based on an inductive element (induction type element), and FIG. 15 shows the structure of the composite head which is viewed from the magnetic recording medium confronting face (generally called as xe2x80x9cair bearing surface [ABS]xe2x80x9d).
A magnetic shield 21 is formed on a base 31 serving as a slider, and an MR element is formed through an insulating layer used to establish electrical insulation. The MR element has a central area 22 for sensing the magnetic field from the magnetic recording medium, and an end portion area 23 comprising a ferromagnetic layer for applying bias magnetic field to the central area 22 and a conductive layer for supplying current. A magnetic shield 24 is further formed through an insulating layer. The above parts constitute a reproduction element portion
The magnetic shield 24 also functions as one of recording magnetic poles, and it is paired with the other recording magnetic pole 26 formed through a recording gap 25. A coil 30 is provided between the magnetic shield 24 serving as one recording magnetic pole and the other recording magnetic pole 26 so as to be located slightly inside away from the ABS while insulated by insulators 28, 29 such as photoresist or the like, and these recording magnetic poles are exited (magnetized) by the magnetic field occurring when current flows through the coil. The above parts constitute a recording element portion.
Recently, much attention has been paid to a GMR head which aims to enhance the recording density by using a giant magnetoresistance effect film (GMR film) at the central area of the MR head to further increase the output power. With respect to the GMR film, particularly a magnetoresistance effect, generally called as xe2x80x9cspin valve effectxe2x80x9d in which the resistance variation corresponds to the cosine defined by the magnetization directions of two adjacent magnetic layers is starting to be practically applied to next-generation MR heads because a large resistance variation can be obtained by a small operating magnetic field. The MR head using the spin valve effect is described in a paper titled xe2x80x9cDesign, Fabrication and Testing of Spin-Valve Read Heads for High Density Recordingxe2x80x9d, IEEE Trans. on Magn., Vol. 30, No. 6 (1994) 3801. The resistance variation rate of the GMR film using the spin valve is equal to about ten and several % at maximum, and thus the practical value in consideration of noises of a magnetic head (hereinafter merely referred to as xe2x80x9cheadxe2x80x9d) is equal to about 7%.
A ferromagnetic tunnel junction element has such a structure that a tunnel barrier layer formed of an extremely thin insulator of nano-meter order is sandwiched between two ferromagnetic layers. According to the ferromagnetic tunnel junction element, when an external magnetic field is applied in the direction along the ferromagnetic layers while fixed current flows between the ferromagnetic layers sandwiching the tunnel barrier layer from both the sides thereof, there appears a magnetoresistance effect corresponding to the relative angle between the magnetization directions of the ferromagnetic layers (this phenomenon is hereinafter referred to as Recently, it has been reported that a magnetoresistance element exhibiting a magnetoresistance variation rate exceeding 20% is achieved by using a surface oxide film of Al as a tunnel barrier layer. For example, xe2x80x9cJournal of Applied Physics, vol. 79, pp4724 to 4729, April 1996xe2x80x9d has reported such a large magnetoresistance variation rate. According to this publication, a first ferromagnetic layer of CoFe is formed on a glass substrate by a vacuum deposition method using a deposition mask, and then the mask is exchanged by another to form an Al layer of 1.2 to 2.0 nm in thickness by the vacuum deposition method. The surface of the Al layer thus formed is exposed to oxygen to form a tunnel barrier layer made of alumina. Finally, a second ferromagnetic layer of Co is formed so as to be superposed on the first ferromagnetic layer through the tunnel barrier layer, thereby completing a cross-shaped electrode type ferromagnetic tunnel junction element. According to this method, it has been theoretically expected that the magnetoresistance variation rate of about 50% is achievable.
By applying the element using TMR as described above to a reproduction head, a magnetic head of higher output power than GMR can be implemented. However, IVR as described above needs to apply a voltage across two adjacent ferromagnetic layers between which an extremely thin insulating layer of 2 nm or less is sandwiched, and thus it has an extremely high risk of dielectric breakdown. Particularly the head to which the structure shown in FIGS. 14 and 15 is applied has a higher risk of electrostatic breakdown of the tunnel barrier layer because the end face of the laminate film of TMR is exposed at the medium confronting face.
Therefore, an object of the present invention is to provide a magnetic head which can suppress occurrence of dielectric breakdown of a tunnel barrier layer while using TRR having a magnetoresistance variation higher than conventional GMR.
Further, another object of the present invention is to provide a composite magnetic head having a TMR reproducing magnetic head and an inductive recording magnetic head in which low-noise reproduction can be performed even when the gap between the head and a magnetic recording medium is small.
Still further, another object of the present invention is to provide a composite magnetic head having an inductive recording magnetic head and a TMR reproducing magnetic head in which high-density recording of a narrow track width can be performed on a magnetic recording medium.
In addition, a further object of the present invention is to provide a method of manufacturing the magnetic head as described above.
A further object of the present invention is to provide a magnetic recording/reproducing apparatus using the magnetic head as described above.
In order to attain the above objects, according to a first aspect of the present invention, there is provided a magnetic head comprising: a magnetic yoke film (magnetic yoke) forming a closed magnetic circuit containing a magnetic gap; a first magnetic layer which is laminated on the magnetic yoke film and magnetically coupled to the magnetic yoke film; a second magnetic layer laminated on the first magnetic layer through a magnetic separation layer; and a pair of electrodes which are formed so that the laminate comprising the magnetic yoke film, the first magnetic layer, the magnetic separation layer and the second magnetic layer is sandwiched therebetween, wherein a magnetic signal in the magnetic yoke film is detected by using a magnetoresistance effect based on the difference between the magnetization direction of the first magnetic layer and the magnetization direction of the second magnetic layer.
In an embodiment of the present invention, the magnetization direction of the second magnetic layer is fixed by laminating an antiferromagnetic layer on the second magnetic layer. In an embodiment of the present invention, a bias magnetic field is applied to the first magnetic layer by a permanent magnet film disposed adjacent to the first magnetic layer in respect of the direction parallel to the surface of the first magnetic layer. In an embodiment of the present invention, the magnetic separation layer is formed of an insulating material, tunnel current is made to flow between the pair of electrodes through the magnetic separation layer, and there is used a ferromagnetic tunnel magnetoresistance effect that the tunnel current is varied in accordance with variation of the difference between the magnetization direction of the first magnetic layer and the magnetization direction of the second magnetic layer. In an embodiment of the present invention, a coil is wound around the magnetic yoke film.
According to a second aspect of the present invention, there is provided a method for manufacturing the magnetic head of the first aspect of the present invention comprising the steps of:
forming a coil lower side portion on a substrate, and forming a lower side insulating film on the coil lower side portion so as to cover the coil lower side portion;
forming a lower side electrode of the pair of electrodes on the lower side insulating film;
forming the magnetic yoke film on the lower side electrode;
laminating on the magnetic yoke film the first magnetic layer, the magnetic separation layer, the second magnetic layer and an antiferromagnetic layer for fixing the magnetization direction of the second magnetic layer;
forming a permanent magnet film for applying a bias magnetic field to the first magnetic layer so that the permanent magnet film is adjacent to the first magnetic layer in respect of the film surface direction of the first magnetic layer; and
forming an upper side electrode of the pair of electrodes so that the upper side electrode is connected to the second magnetic layer, and forming a coil upper side portion so that the coil upper side portion is connected to the coil lower side portion so as to form a coil wound around the magnetic yoke film.
In an embodiment of the present invention, the magnetic gap of the magnetic yoke film is formed by an etching treatment using a focused ion beam. In an embodiment of the present invention, when forming the upper side electrode and forming the coil upper side portion, after an upper side insulating film is formed on the overall surface, openings are formed at the portion of the upper side insulating film corresponding to the antiferromagnetic layer and the portion corresponding to the connection portion of the coil lower side portion with the coil upper side portion, a conductive film is formed and then the conductive film is patterned.
According to a third aspect of the present invention, there is provided a magnetic head comprising: a first magnetic layer serving as a magnetic yoke film (magnetic yoke) forming a closed magnetic circuit containing a magnetic gap; a second magnetic layer laminated on the first magnetic layer through a magnetic separation layer; and a pair of electrodes formed so that the laminate comprising the first magnetic layer, the magnetic separation layer and the second magnetic layer is sandwiched by the electrodes, wherein a magnetic signal in the magnetic yoke film is detected by using a magnetoresistance effect based on the difference between the magnetization direction of the first magnetic layer and the magnetization direction of the second magnetic layer.
In an embodiment of the present invention, the magnetization direction of the second magnetic layer is fixed by laminating an antiferromagnetic layer on the second magnetic layer. In an embodiment of the present invention, a bias magnetic field is applied to the first magnetic layer by a permanent magnet film disposed adjacent to the first magnetic layer in respect of the direction parallel to the surface of the first magnetic layer. In an embodiment of the present invention, the magnetic separation layer is formed of an insulating material, tunnel current is made to flow between the pair of electrodes through the magnetic separation layer, and there is used a ferromagnetic tunnel magnetoresistance effect that the tunnel current is varied in accordance with variation of the difference between the magnetization direction of the first magnetic layer and the magnetization direction of the second magnetic layer. In an embodiment of the present invention, a coil is wound around the magnetic yoke film.
According to a fourth aspect of the present invention, there is provided a method of manufacturing the magnetic head of the third aspect of the present invention comprising the steps of:
forming a coil lower side portion on a substrate, and then forming a lower side insulating film on the coil lower side portion so that the lower side insulating film covers the coil lower side portion;
forming a lower side electrode of the pair of electrodes on the lower side insulating film;
forming the magnetic yoke film serving as the first magnetic layer on the lower side electrode, and then laminating the magnetic separation layer, the second magnetic layer and the antiferromagnetic layer for fixing the magnetization direction of the second magnetic layer;
forming the permanent magnet film for applying a bias magnetic field to the first magnetic layer so that the permanent magnetic film is adjacent to the first magnetic layer in respect of the film surface direction of the first magnetic layer; and
forming an upper side electrode of the pair of electrodes so that the upper side electrode is connected to the second magnetic layer, and then forming a coil upper side portion so that the coil upper side portion is connected to the coil lower side portion to form a coil wound around the magnetic yoke film.
In an embodiment of the present invention, the magnetic gap of the magnetic yoke film is formed by an etching treatment using a focused ion beam. In an embodiment of the present invention, when forming the upper side electrode and forming the coil upper side portion, after the upper side insulating film is formed on the overall surface, openings are formed at the portion of the upper side insulating film corresponding to the antiferromagnetic layer and the portion corresponding to the connection portion of the coil lower side portion with the coil upper side portion, a conductive film is formed and then the conductive film is patterned.
According to a fifth aspect of the present invention, a magnetic recording/reproducing apparatus for recording/reproducing information through a magnetic head on/from a magnetic recording medium, is characterized in that the magnetic head is any one of the magnetic head of the first or third aspect of the present invention, and the magnetic head is movable along the surface of the magnetic yoke film relatively to the magnetic recording medium.
In an embodiment of the present invention, the information is recorded/reproduced while the gap between the magnetic recording medium and the magnetic head is kept to be 40 nm or less. In an embodiment of the present invention, the magnetic recording medium is a flexible tape-shaped medium obtained by forming a magnetic recording layer on a flexible substrate, a flexible disc-shaped medium obtained by forming a magnetic recording layer on a flexible substrate, or a medium obtained by forming a magnetic recording layer on a substrate of a rigid body. In an embodiment of the present invention, the magnetic recording layer is a magnetic thin film formed by a physical vapor deposition method.
According to the present invention, not only a magnetic head which suppresses occurrence of the electrostatic breakdown of the tunnel barrier layer can be provided while using TMR which gains a magnetoresistance variation exceeding that of conventional GMR, but also the recording track width corresponding to the thickness of the magnetic yoke film can be obtained, so that a magnetic head capable of realizing an extremely small track width can be implemented. Further, the magnetic yoke for the recording element is also used as the magnetic yoke for the reproducing element, so that the number of manufacturing steps can be reduced and the cost can be easily lowered.
Further, in the case of TMR, the resistance value of the element also reflects the resistance of the tunnel barrier layer serving as the insulator, and thus the resistance value of the element is liable to be high. However, according to the present invention, the area of the TPR film can be set to be relatively large, so that the resistance value of the element can be sufficiently reduced.
As described above, according to the present invention, there can be implemented a magnetic head which can reduce the number of manufacturing steps, lower the manufacturing cost, facilitate the narrow track design and suppress noises appending to the conventional MR head such as thermal asperity even in a high-density magnetic recording/reproducing area where the gap between the magnetic recording medium and the head is equal to 40 nm or less, by using DZR having a large magnetoresistance variation exceeding that of conventional GMR and commonly using the magnetic yoke for recording and reproduction. In addition, according to the present invention, there can be implemented a magnetic recording/reproducing apparatus using such a magnetic head. Further, according to the magnetic head of the present invention, the TMR film is not exposed at the medium confronting face, so that occurrence of the electrostatic breakdown of the tunnel barrier layer can be suppressed.